In the telecommunications industry and more particularly in the video transmission industry, signals (e.g., 5 MHz to 1 GHz) are carried over coax conductors from a headend to customers. At the headend of the systems, numerous signals are manipulated to achieve a wide variety of functions and objectives. For example, signals carried on numerous coax cables may be combined onto a single coax conductor. Similarly, a signal on a main coax conductor may be divided into a plurality of signals carried on branch coax conductors.
In addition to combining, splitting, diverting or adding signals, the headend will also include a module for modifying signals. For example, in order to adequately tune the system, it may be desirable to provide attenuators or the like to attenuate a signal to a desired level. Further, as a broadband RF signal is carried over a length of cable, the high frequency range of the signal may be attenuated more than a low frequency range of the signal. As a result, equalizers are utilized to modify the signal to have a level intensity throughout its frequency range.
Frequently, tuning is accomplished through the use of plug-in devices (e.g., attenuators or equalizers). Exemplary systems including plug-in devices are disclosed in U.S. Pat. No. 6,289,210 which is hereby incorporated by reference.
Typically, a module such as a combiner has receptacles mounted on a printed circuit board. Terminals of a plug extend into a receptacle and are electrically coupled to the circuit board by electrical components that are all located on the same side of the circuit board. In particular, electrical components communicate with the receptacle and electrically couple terminals of a plug to the proper layer of the circuit board using vias, for example, if necessary. This style of mounting increases the amount of signal radiating around the electrical components causing cross talk in adjacent circuits. Also, because the leads of the electrical components are inductive, special circuit designs are used to compensate.
It is desirable to improve the amount of isolation between adjacent ports on a module. In addition, it is desirable to reduce parasitics that reduce loss of a specific port and increase insertion loss.
It is important to provide electromagnetic shielding to modules that house electrical components. For example, in a combiner module, a plurality of attenuator plugs that house circuitry are inserted in one side of the module. For example, a plurality of attenuator plugs may be inserted in receptacles of the housing. Once the plugs are inserted, a conductive cover is placed over the plug and receptacles to shield the circuit board from the outside environment and vice versa. When the cover is removed for maintenance, for example, the module radiates signals into the outside environment about 60 dB down from the carrier. Such radiation interferes with the operation of the headend. Sometimes, it is possible that the cover is not replaced after the maintenance is completed. Other times the repairs may take hours to perform while the cover must remain off.
It is desirable to provide a module in which such emissions are at least 100 dB down from the carrier so that the possibility of interference is reduced. In addition, it is desirable to provide a module with improved shielding.